BLOCKING AND INTERMITTENT UNLOCKING OF NOISE IMPULSE IN DIGITAL SUBSCRIBER LINE SYSTEMS (DSL)
TECHNICAL FIELD The invention relates generally to a communication system and, more particularly, to blocking and unblocking impulse noise in a communication system.
BACKGROUND OF THE INVENTION There are several types of noise sources and interference in multi-carrier communication systems, such as a Discrete Multiple Tone (DMT) system. The interference and noise can corrupt the data carrier signal over a subchannel tone (often referred to as a tone) that the signal travels through the communication channel and is decoded in the receiver. The transmitted data carrier signal can be mistakenly decoded by the receiver due to this corruption of the signal. The number of data bits or the amount of information a subchannel contains can vary from subchannel to subchannel and depends on the relative power of the data carrier signal compared to the power of the corruption signal on that particular subchannel. To account for potential interference on the transmission line and to ensure reliable communication between the transmitter and receiver, each sub-channel of a DMT system is typically designed to contain a limited number of data bits per unit time based on
The Signal-to-Noise Ratio (SNR) of the sub-channel using a bit-loading algorithm, which is an algorithm for determining the number of bits to be assigned to each sub-channel. The number of bits that a specific sub-channel can contain while maintaining an objective bit error percentage (BER) decreases as the relative strength of the corruption signal increases, ie when the SNR decreases. In this way, the SNR of a sub-channel can be used to determine how much data should be transmitted on the sub-channel to maintain a target bit error rate. It is often assumed that the corruption signal is an additive random source with Gaussian distribution and white spectrum. With this assumption, the number of data bits that each subchannel can contain is directly related to the SNR. However, this assumption may not be true in many practical cases and there are several sources of interference that do not have a white Gaussian distribution. Impulse noise is one of those sources of noise. Bit load algorithms are usually designed based on the assumption of Gaussian noise, white, additive. With these algorithms, the effects of impulse noise can be underestimated resulting in an excessive error rate during the actual data transmission. In addition, channel estimation procedures can be designed to optimize performance in the presence of stationary damage such as Gaussian, white, additive noise, but are often poor for estimating non-stationary or stationary cycle damage, such as impulse noise. As a result, Digital Subscriber Line (DSL) modem training procedures are typically well suited to optimize the
performance in the presence of Gaussian noise, white, additive, but leave modem receivers relatively defenseless to impulse noise.
BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention are illustrated by way of example and without limitation in the Figures of the accompanying drawings, in which similar references indicate similar elements and in which: Figure 1 illustrates a schematic diagram of one mode of a DSL system; Figure 2 illustrates a schematic diagram of a digital communication system in which an embodiment of the invention can be implemented; Figure 3 illustrates a schematic diagram showing a mode of a receiver performing the blocking and unlocking of the impulse noise; Figure 4 illustrates a schematic diagram showing one embodiment of a system for effecting locking and unlocking of impulse noise y; Figure 5 illustrates the mode of a method of locking and unlocking impulse noise in a DSL system.
DETAILED DESCRIPTION In the following description, for explanation purposes, numerous specific details are exposed to provide a better
understanding of the invention. It will be clear, however, to one skilled in the art that the invention can be practiced without those specific details. In other cases, well-known circuits, structures and techniques are not shown in detail or shown in block diagram form to avoid unnecessarily obscuring the understanding of this description. Impulse Noise can be difficult damage or deterioration for DSL modems. Impulse noise lasting tens of microseconds can cause errors in all subchannels used in the receiver. In addition, impulse noise can have bursts of power that are much greater than the level of background noise causing significant loss of performance. These bursts of power can have a very small duty cycle so that they do not contribute significantly to the average noise power. This can result in an aggressive bit loading on some or all of the DMT system subchannels, which would result in a high bit error rate much higher than that of the target BER. Impulse noise is a corruption signal that is typically considered difficult to correct and compensate for. For example, the noise pulse can affect and deflect the measurements made by a communication system with respect to the quality of the received signal. Examples of these measurements include power-to-noise measurements and timing synchronization measurements. Because these measurements are used to fine-tune, adapt and fine-tune any of the parameters for optimal operation of the communication system, impulse noise can result in a non-optimal adaptation of the communication system to changes in quality of the
received signal. The embodiments of the invention can be related to any communication system, and in particular to a multi-carrier system in which non-Gaussian noise such as the noise pulse, which affects a received signal can be beneficial. Figure 1 shows a DSL system 100. The DSL system 100 consists of a local circuit 110 (telephone line) with a transceiver (also known as a modem) at each end of the wires. The transceiver at the end of the line 150 network is known as the central end transmission unit (TU-C) 120. The TU-C 120 may reside within a DSL access multiplexer (DSLAM) or a remote terminal of digital circuit carrier (DLC-RT) for lines powered from a remote site. The transceiver at the end of the client or user 160 of the line is known as the remote end transmission unit (TU-R) 130. Figure 1 also shows terminal equipment 140, which is the end-user's equipment, as a personal computer or a telephone. Figure 2 illustrates a block diagram of a modality of a Discrete Multiple Tone system. The Discrete Multiple Tone system 400, as a network based on a Digital Subscriber Line (DSL), may have two or more transceivers 402 and 404, such as a DSL modem in a decoder. In one embodiment, the decoder can be a stand-alone DSL modem. In one embodiment, for example, the decoder uses a DSL mode together with other media components to combine television (Internet Protocol or Satellite TV) with broadband content of the Internet to carry the
commercial video communications and the Internet to a TV set of the end user. The multi-carrier communication channel can communicate a signal to a residential house. The house can have a local network, like an ethernet. The local network can use the multi-carrier communication signal directly, or convert the data of the multi-carrier communication signal. The decoder can also include an integrated Satellite and Digital TV Receiver, High Definition Digital Video Registration, Digital Media Server and other components. The first transceiver 402, like the Discrete Multlone Transmitter, which i transmits and receives communication signals from the second transceiver 404 on a transmission medium 406, such as a telephone line. Other devices, such as telephones 408, can also be connected to this transmission means 406. Generally, there is an insulating filter 410 between the telephone 408 and the transmission medium 406. A training period occurs when they are established.
Initially communications between the first transceiver 402 and a second transceiver 404. The Discrete Multiple Tone system 400 can include a central office, multiple distribution points, and multiple end users. The central office can contain the first transceiver. 402 to contact the
second transceiver 404 at the location of the end user. Each portion of the transmitter 417, 419 of the transceivers 402, 404, respectively, can transmit data over a number of subchannels, i.e., mutually independent tones. Each subchannel contains or transports only a certain portion of the data through a modulation scheme, such as
Quadrature Amplitude Modulation (QAM) of the subcarrier. The number of information bits loaded on each subchannel and the size of the corresponding QAM constellation can potentially vary from one subchannel to another and generally depends on the relative power of the signal and the noise at the receiver. When the characteristics of the signal and noise are known for all subchannels, a bit-loading algorithm can determine the optimal distribution of the data bits and the signal strength between the sub-channels. In this way, a portion of the transmitter 417, 419, of the transceivers 402, 404, modulates each subcarrier with a data point in a QAM constellation. Each transceiver 402, 404 also includes a portion of the receiver
418, 416, which contains physical computing or hardware components and / or programming and software systems or software in the form of software programs and systems and / or physical computing or hardware components to detect the presence of present impulse noise. in the communication channel. The pulse detector 116, 118 detects the presence of impulse noise in the communication channel over finite time intervals known as frames or frames (or simply frames or frames). Figure 3 illustrates a mode of a receiver of Figure 2. In this mode, the receiver 416 can contain several modules such as a Fast Fourier Transform (FFT) 710 module, filters 712, a Gaussian Noise Detector 714, a Detector of Non-Gaussian Noise 716, a measurement and adaptation module 718, a SNR module 722 and a bit loading module 724. Additional modules and functionalities may exist in the receiver 416 that were not illustrated so as not to obscure the understanding of the modalities of the invention.
Furthermore, although certain modules and functionalities are illustrated as if they existed in the receiver 416, the modules and functionality can be physically distributed outside the receiver 416. For example, measurement and adaptation operations of the measurement and adaptation module 718 can be implemented in modules separated. Also, it should be noted that the operations of one or more modules can be incorporated into or integrated with other modules. At receiver 416, the data of each subchannel is typically extracted from the time domain data following the Fourier transformation of a block of samples of the multicarrier signal. The Fast Fourier Transformation module 710 receives the output of a set of filters 712 which are used to exclude out-of-spectrum signals from the transmission channel. The Fast Fourier Transformation module 710 transforms the data samples of the multi-carrier signal from the time domain to the frequency domain, so that a data stream of each subcarrier can be sent from the Fast Fourier Transformation module 710. Essentially, the Fast Fourier Transformation module 710 acts as a demodulator to separate the data corresponding to each subchannel into multiple tone signals. The output of the FFT 710 is transmitted to a Frequency Domain Iguager 726, which corrects for gain effects and phase deviation of the transmission channel. These effects are determined at the modem receiver during transmission by comparing the measured signal sent from the FFT to the expected outputs. The Frequency Domain IgG performs a gain and phase correction on each FFT subchannel output so that each subchannel is free of gain and phase errors; those factors of
Corrections need to be adjusted during data transmission because the transmission channel can change slowly over time. The output of the Frequency Domain IgG is sent to a Gaussian noise detector 714, a non-Gaussian noise detector 716 and the measurement and adaptation module 718. During a training session, for example, between the transceiver in an office central (e.g., transceiver 402) and the transceiver at the end user's location (e.g., transceiver 404), the transmitter portion (e.g., transmitter 417) of the transceiver at the central office broadcasts long sequences including each one of those data points. Over time, a large number of samples are collected for each potential data point. The Gaussian noise detector 714 measures the power of Gaussian noise in a subcarrier signal. For each particular subcarrier of the multicarrier signal, the Gaussian noise detector 714 measures the power level of the total noise for that subcarrier. The Gaussian noise detector 714 includes a decoder module of the expected transmitted data points. The Gaussian noise detector module 714 measures the Gaussian noise present in the system by comparing the average difference between the values of the received data with a finite set of expected data points that can potentially be received. The noise in the signal can be detected by determining the distance between the determined transmitted point (a particular amplitude and phase of the subcarrier for the data frame or frame) to the received point to determine the power of the error signal for that subcarrier in that frame from
data. The present noise produces the error between the expected known value and the actual received value. For each particular subcarrier of the multicarrier signal, the non-Gaussian noise detector 716 measures the power level of the total noise for that subcarrier including any impulse noise. If non-Gaussian noise is present, then the non-Gaussian noise detector 716 activates non-Gaussian noise compensation to provide information about the contribution of non-Gaussian noise to the measurement and adaptation module 718 to achieve a bit percentage more optimal than the which can be transported by a subchannel. If pulse noise is present, the measurement and adaptation module 718 can generate measurements, for example, measurements to be used in the calculation of the SNR and the subsequent bit load algorithm for that sub-channel, as noise power measurements. , timing synchronization measurements and equalizer quality measurements, without using the corrupted samples in the measurements. The measurement and adaptation module 718 can also not use the corrupted data in the fine tuning of the parameters of the DSL modem. The adaptation and verification signals produced by the measurement and adaptation module 718 can be fed back into the receiver, for example, to determine the bit-loading algorithm for a sub-channel. The measurement and adaptation module 718 can also collect and track the statistical information related to the impulse noise. This information can be used to characterize the nature of impulse noise
on the line and can provide guides to adjust some of the parameters of the modem that provide more flexibility towards impulse noise. For example, the measurement and adaptation module 718 can identify the duration of the impulse noise and its frequency. This data can be used to verify the quality of the communication channel. They can also be used to set the minimum requirement for the value of the noise margin and protection against impulse noise. The noise power, for example, as measured by the measurement and adaptation module 718, and the signal power, for example, as measured by the power measurement module of the 720 signal, can be fed to the Signal to Noise Ratio (SNR) block 722. In certain embodiments, the equivalent noise power calculation can include the calculation of the noise power made by the noise detector of the signal 708. The block of SNR determines a signal-to-noise ratio, which is used to determine the bit load 724 for the subcarrier. The Signal Power Measurement Module 716 measures the power of the subcarrier signal, and feeds the result to the SNR 722 module. The SNR 722 module determines a signal-to-noise ratio using the equivalent noise power provided by the detector 720. The signal to noise ratio is provided to the bit load module 724 to determine the bit load for all those subcarriers. The bit percentage for a subchannel determined by the bit loading module can then be transmitted, using the transmitting portion 419, to the transceiver 402 (eg, in the central office) to allow the transmitter 417 of the transceiver 402 to know
how many bits to use on each subchannel. Figure 4 illustrates another embodiment of a receiver of Figure 2. In this mode, the receiver 416 analyzes the received signal to determine an error in the signal transmitted by the transceiver 402 and the signal received by the receiver 416. A noise detector non-Gaussian 716 analyzes the detection error to detect the presence of non-Gaussian noise, such as impulse noise. If that noise is detected, the non-Gaussian noise detector 716 can activate the measurement and adaptation module 718 to avoid an adjustment of a quality measurement of the received signal. The non-Gaussian noise detector 716 can activate the measurement and adaptation module 718 to prevent tuning of the parameters of the DSL modem. If no impulse noise is detected, the measurement and adaptation module 718 continues to adjust the quality measurements (such as noise power measurements, timing synchronization measurements and equalizer accuracy measurements) and adjusts the tuning of the parameters of the DSL modem. Figure 5 illustrates an embodiment of a method of blocking and releasing impulse noise in a DSL 400 system. In block 610, a quality measurement of a received signal on a communication channel is determined. The quality measurement is used to tune to one or more parameters of the DSL modem. In block 620, the presence of non-Gaussian noise including impulse noise in the system is detected or estimated. For example, a burst of corruption noise in the received signal can be detected by observing a high noise power through several subcarriers, which is an unlikely event with white Gaussian noise. In block 630,
it prevents an adjustment of a quality measurement of a signal based on the detection of the corruption noise burst. Consequently, the measurement modules in the DSL modem are activated to avoid the use of corrupted samples in their measurements, such as noise power measurements, timing synchronization measurements and equalizer accuracy measurements. In block 640, an adjustment of the tuning parameters of the DSL modem is prevented based on the detection of the corruption noise burst. Consequently, the adaptation modules in the DSL modem are activated to avoid the use of corrupted samples in their fine tuning of the parameters of the DSL modem. In this way, the blocking and unblocking of pulses can avoid errors in the measurements, such as noise power measurements, timing synchronization measurements and equalizer accuracy measurements, and allow a better and more stable and more robust adaptation of the parameters of the modem. In this way, a method of locking and unlocking noise pulses is described here. The methods described herein can be performed in a means accessible by a machine, for example, to effect blocking and unlocking of noise pulses. A means accessible by a machine includes any mechanism that provides (e.g., stores and / or transmits) information in a form accessible by a machine (e.g., a computer). For example, a medium accessible by a machine includes a read-only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; instant memory devices; DVD, electrical, optical, acoustic signals u
another form of propagated signals (for example, carrier waves, infrared signals, digital signals, EPROM, EEPROM, FLASH, magnetic or optical cards, or any type of suitable medium for storing electronic instructions.) The data representing the devices and / or methods stored in the medium accessible by a machine can be used to make the machine perform the methods described here.The reference in the description to "one modality" or "modality" means that one featureThe particular structure or feature described in relation to the embodiment are included in at least one embodiment of the invention. The occurrence of the phrase "in one modality" in several places in the specification does not necessarily refer entirely to the same modality. The term "coupled" as used herein may include directly coupled and indirectly coupled through one or more intervening components. Although the methods of locking and unlocking of noise pulses have been shown in the form of a flowchart having separate blocks and rows, the operations described in a single block do not necessarily constitute a process or function that is dependent or independent of the other operations described in the other blocks. In addition, the order in which the operations are described here is merely illustrative, and not limiting of the order in which those operations may occur in alternative modes. For example, some of the operations described may occur in series or in parallel, or alternately and / or iteratively. Although some specific embodiments of the invention have been shown, it is not limited to these modalities. It must be understood that the
invention is not limited by the specific embodiments described herein, but only by the scope of the appended claims. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.